Bug 764

Bug Description:

This is a deadlock.
The following is an example of deadlock thread dump:

"Thread-1": waiting to lock monitor 0x0000000008b6eab8 (object 0x00000000ec6105a8, 
    a org.apache.derby.impl.services.reflect.UpdateLoader), which is held by "Thread-0"
"Thread-0": waiting to lock monitor 0x000000000bafb528 (object 0x00000000ed2e6298, 
    a org.apache.derby.impl.services.locks.LockSet), which is held by "Thread-1"
    
Java stack information for the threads listed above:
===================================================
"Thread-1":
    at org.apache.derby.impl.services.reflect.UpdateLoader.needReload(UpdateLoader.java:366)
    - waiting to lock <0x00000000ec6105a8> (a org.apache.derby.impl.services.reflect.UpdateLoader)
    at org.apache.derby.impl.services.reflect.ClassLoaderLock.unlockEvent(UpdateLoader.java:434)
    at org.apache.derby.impl.services.locks.Lock.unlock(Lock.java:131)
    at org.apache.derby.impl.services.locks.Lock.unlock(Lock.java:208)
    at org.apache.derby.impl.services.locks.LockSet.unlock(LockSet.java:521)
    - locked <0x00000000ed2e6298> (a org.apache.derby.impl.services.locks.LockSet)
    at org.apache.derby.impl.services.locks.LockSpace.unlockGroup(LockSpace.java:147)
    - locked <0x00000000ec6daa78> (a org.apache.derby.impl.services.locks.LockSpace)
    at org.apache.derby.impl.services.locks.AbstractPool.unlockGroup(AbstractPool.java:214)
    at org.apache.derby.impl.services.locks.LockOperator.unlock(LockOperator.java:32)
    at org.apache.derby.impl.services.reflect.Derby764$Thread2.run(Derby764.java:62)

"Thread-0":
    at org.apache.derby.impl.services.locks.LockSet.lockObject(LockSet.java:148)
    - waiting to lock <0x00000000ed2e6298> (a org.apache.derby.impl.services.locks.LockSet)
    at org.apache.derby.impl.services.locks.AbstractPool.lockObject(AbstractPool.java:119)
    at org.apache.derby.impl.services.reflect.UpdateLoader.lockClassLoader(UpdateLoader.java:326)
    at org.apache.derby.impl.services.reflect.UpdateLoader.modifyJar(UpdateLoader.java:290)
    - locked <0x00000000ec6105a8> (a org.apache.derby.impl.services.reflect.UpdateLoader)
    at org.apache.derby.impl.services.reflect.Derby764$Thread1.run(Derby764.java:47)
	

How To Reproduce:

This bug is reproduced under derby 10.5.1.1 and JDK 1.6.0_33.
Execute the following scripts to run the test to reproduce the bug (assume the location of the derby test project is derby_test_home).

Linux:
${derby_test_home}/scripts/764.sh
Windows:
%derby_test_home%\scripts\764.bat